Receivers in digital communications systems are used to detect and extract information or data signals from a received signal. A variety of effects may reduce the performance of a receiver. These include noise, one or more nonlinearities, and one or more spurious signals associated with a communication channel between a transmitter and the receiver. The spurious signals may include interference signals, such as one or more echoes or multi-path signals.
Multi-path signals are often associated with reflections from objects in the communication channel. In general, a respective multi-path signal may have a different amplitude than a desired signal and/or may be phase or time shifted relative to the desired signal. The time shift may be positive or negative, i.e., the respective multi-path signal may lead or lag the desired signal. Such multi-path signals are referred to as a pre-multi-path signal and a post-multi-path signal, respectively.
Unfortunately, multi-path signals may be problematic for conventional receivers. Multi-path signals often contain similar spectral content to the desired signal. Indeed, the multi-path signals often resemble the desired signal. Multi-path signals may vary as a function of time, for example, due to motion of the transmitter and/or receiver, or other changes in the communication channel. Conventional receivers may have difficulty in reliably detecting the desired signals in the presence of one or more pre-multi-path signals and/or one or more post-multi-path signals.
Accordingly, there is a need for improved receivers that can reliably detect desired signals in the presence of multi-path signals.